Mobile stations, also known as mobile terminals, wireless terminals and/or user equipments (UE) are enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The communication may be made e.g. between two mobile stations, between a mobile station and a regular telephone and/or between a mobile station and a server via a Radio Access Network (RAN) and possibly one or more core networks.
The mobile stations may further be referred to as mobile telephones, cellular telephones, laptops with wireless capability. The mobile stations in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another mobile station or a server.
The wireless communication system covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g. a Radio Base Station (RBS), which in some networks may be referred to as “eNB”, “eNodeB”, “NodeB” or “B node”, depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. The base stations communicate over the air interface operating on radio frequencies with the mobile stations within range of the base stations.
In some radio access networks, several base stations may be connected, e.g. by landlines or microwave, to a Radio Network Controller (RNC) e.g. in Universal Mobile Telecommunications System (UMTS). The RNC, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Special Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be connected to a gateway e.g. a radio access gateway. The radio network controllers may be connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for mobile stations. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
According to 3GPP/GERAN, a mobile station has a multi-slot class, which determines the maximum transfer rate in the uplink and downlink direction. GERAN is an abbreviation for GSM EDGE Radio Access Network. EDGE is further an abbreviation for Enhanced Data rates for GSM Evolution.
In the present context, the expression downlink is used for the transmission path from the base station to the mobile station. The expression uplink is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
A maximum downlink and uplink rate may, for many multi-slot classes, not be reached simultaneously due to the nature of the specified multi-slot classes. The GERAN has to decide which direction to prioritize, uplink or downlink, and give the maximum bandwidth to either uplink or downlink, not to both at the same time.
The transmission of signals between a mobile station and a base station may be made on a carrier. A frame is subdivided into timeslots, which may be allocated for either uplink or downlink transmission.
An algorithm to determine the main direction of the data flow, i.e. uplink or downlink of a packet based session may be utilized. However in many cases the algorithm cannot be fast enough to fully utilize the bandwidth according to the multi-slot capability of the mobile station. Many interactive packet switched services require uploads and downloads of data, but not simultaneously. The services may be interactive in the sense that an upload is responded by a download and vice versa. Such fast shift in bandwidth demands, from uplink to downlink and vice versa, is made possible with Enhanced Flexible Timeslot Assignment (EFTA), which was comprised in 3GPP/GERAN Release-9. EFTA makes a full utilization of the bandwidth possible, and provide thereby a more efficient packet switched service. Another feature that is made possible with EFTA is the support and use of more than 5 timeslots per carrier for a mobile station and direction, downlink and uplink. Without EFTA, this is not possible in practice today, since support for “Type 2” mobile stations is considered very complex and expensive to implement in mobile stations.
In order to provide required data bandwidth, several carriers may be used in a process called carrier aggregation. A type 1 system and a type 2 system are classified according to whether carrier aggregation is used. By using carrier aggregation, several carriers are aggregated on the physical layer to provide the required bandwidth.
A shared component carrier is used for both a type 1 mobile station and a type 2 mobile station, whereas a dedicated component carrier is used only for the type 2 mobile station. Also, a type 2 base station transmits broadcast information by using a shared component carrier. In this instance, the broadcast information comprises the shared broadcast information used for both the type 1 mobile station and the type 2 mobile station and the dedicated broadcast information only for the type 2 mobile station. Additionally, the type 2 base station indicates component carriers that are used by the type 2 mobile station, by using a semi-static component carrier indicator or a dynamic component carrier indicator.
When more than 5 timeslots are supported and used e.g. within an EFTA system, uplink and downlink blocks have the risk of “colliding”, i.e. that timeslots are allocated both for uplink and downlink communication at the same time. Since uplink is prioritized with EFTA, downlink blocks will in such case be lost and need to be re-transmitted. The probability of “collision” is higher or lower depending on chosen Temporary Block Flow (TBF) configuration. It is up to the EFTA Channel Utilisation function to determine the TBF configuration with a number of inputs.
The problem with the existing solution is that since the uplink is prioritized and the uplink scheduling order is pre-defined, i.e. built into EFTA, some TBF configurations will perform considerably worse than other configurations, in the sense that more collisions between uplink and downlink will occur and thus more retransmissions in downlink have to be made.
When using less than 8 timeslots downlink (per carrier), some uplink timeslots will destroy more downlink timeslots than others. When using 8 timeslots downlink (per carrier), some uplink timeslots will destroy more important downlink timeslots than others. Which uplink timeslots that destroys downlink timeslots depend on which timeslots are assigned to the downlink and uplink TBFs.
One method of finding the best possible TBF configuration for EFTA would be to evaluate every possible alternative at every occasion when EFTA TBF is to be assigned. This would however consume a lot of processing power in the base station where the algorithm is implemented. It may also be more time consuming and lead to a general performance degradation within the wireless communication system.
Another solution would be to prohibit the support and use of more than 5 timeslots per carrier for a terminal and direction, downlink and uplink. However, since the uplink typically may not use all assigned timeslots every Transmission Time Interval (TTI), setting restrictions on timeslot reservations would severely affect performance, leading to low utilization of available resources.
Also, the switching time, for switching between receiving and transmitting in uplink/downlink respectively will affect the performance of the method to find the best possible TBF configuration within the wireless communication system resulting in better or worse communication delay.